- The atmosphere has a certain level of carbon-14, and living things stay at the atmospheric level by virtue of the various processes by which they interact with the atmosphere.
- When they stop living, they also stop exchanging carbon with the atmosphere, and their carbon-14 levels change due to radioactive decay over time.
- But here, an environment was sealed off from the atmosphere while some organisms remained alive inside it. If we perform radiocarbon dating on such an organism, will we get the date at which the organism died (and stopped exchanging carbon with anything) or the date at which the environment was sealed (and everything stopped exchanging carbon with the atmosphere)?
Your comment isn't responsive to this question. To answer it, we'd need to know why the atmosphere itself has constant levels of carbon-14 instead of decaying like everything else, and whether the sealed environment would have behaved more like the atmosphere or like something else.
This page is good: https://en.wikipedia.org/wiki/Radiocarbon_dating